A 100 W electric bulb produces electromagnetic radiation with electric field amplitude of 2 V m - 1 at a distance of 10 m . Assuming it as a point source, estimate the efficiency of the bulb.

Question

A 100 W electric bulb produces electromagnetic radiation with electric field amplitude of 2 V m - 1 at a distance of 10 m . Assuming it as a point source, estimate the efficiency of the bulb., 4 . 9 %, 2 . 5 %, 13 . 3 %, 19 . 7 %

MARKS App · Accepted Answer

Intensity = power × η A . . . 1 We know, 1 2 I = 1 2 ε 0 E 2 c I = 8 . 854 × 10 - 12 2 2 3 × 10 8 I = 0 . 0106 w m - 2 . . . 2 On substituting 2 in 1 , 0 . 0106 = 100 × η 4 × π × 10 2 ⇒ η = 0 . 133 = 13 . 3 %

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